Process for making fuel gas from natural gasoline and straight run gasoline



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Paocss Fon MAKING FUEL GAs mou NATURAL GASOLINE AND STRAIGHT RUNGASOLINE Filed Jan. 22, 1948 2 Sheets`Sheet 2 Patented Sept.. 18. 195?`PROCESS FOR MAKING FUEL GAS FROM NATURAL GASOLINE AND STRAIGHT RUNGASOLINE Charles Gordon Milboume, Toledo, Ohio, assignor to SurfaceCombustion Corporation, Toledo, Ohio, a corporation oi' Ohio ApplicationJanuary 22, 1948, Serial No. 3,716

3 Claims. 1

The increased use of manufactured andl natural fuel gas for seasonalheating in urban areas is now taxing the capacity of many utilities tomeet the demand. Various expedients are being utilized such as mixingsemi-gaseous petroleum products, also called liquid petroleum gases,such as propane and butane with air and feeding the mixture intodistributing mains up to a proportion which will not adversely afl'ectthe eiiiciency of the appliances burning these mixed fuels.

More recently there has come into use a process for partially oxidizingor cracking the raw propane or butane with air and steam to m-ake a gaswhich, when cold enriched with additional propane or butane, will yielda fuel gas which in most of its characteristics is comparable with citygas made by the older processes and which is substantially completelyinterchangeable therewith. The advantageof such a process is that acracking plant may be located almost anywhere along a distributionsystem without in any way adversely aiecting the appliances fed by suchsystem. However, propane and butane are true.

gases at normal temperature and pressure; hence when stored in largequantities they must be liquefied under high pressure necessitating amultiplicity of pressure vessels which are comparatively highlyexpensive. In point of fact the cost of providing storage for a wholewinters supply may exceed the total cost of the cracking plant and itsauxiliaries. Furthermore, the cost of these products themselves isgreatly enhanced by havingto provide high pressure transportationfacilities which precludes transportation in bulk.

The present invention has for its object to provide a gas making processwhich shall involve the use of a petroleum feedstock consisting ofgasoline selected from the group consisting of natural gasoline andstraight run gasoline.` Because of its relatively low vapor pressurestraight run gasoline presents no particular shipping and storageproblems such as the use of high pressure storage vessels; nor doesnatural gasoline provided its vapor pressure is not permitted to exceed26` pounds RVP (Reids Vapor Pressure). See A. S. T. M. SpeciiicationD32343.

In the present invention the selected gasoline feedstock is ilrstsubjected to fractional distillation to obtain a rst portion(hereinafter called the enriching portion or fraction) consistingessentially of hydrocarbons lighter than or not heavier than Ce forreasons presently appearing and to obtain a second fraction (hereinaftercalled the cracking portion or fraction) consisting essentially ofhydrocarbons not heavier than Cs for a reason presently appearing. Therem-aining fraction is a still bottoms residue suitable for use as fueloil or as a motor fuel.

The next step is to partially oxidize the cracking portion of thefeedstock with air and/or steam in the presence of a catalyst to producea product gas rich in hydrogen and carbon monoxide. The final step is tocold enrich the partially oxidized product gas with the enrichingportion of the feedstock.

The enriching fraction of the feedstock should not contain anyappreciable concentration of hydrocarbons heavier than Ce primarilybecause a heavier hydrocarbon is likely to condense in the gasdistributing system. For example, la distribution system supplying a 540B. t. u. gas of approximately 0.69 specific gravity normally requires anenriching vapor which will not condense in the gas mains at a groundtemperature of 40 F.; hence, a C7 hydrocarbon, such as heptane. or anyof the heavier hydrocarbons cannot be used for enriching purposesbecause with the proportionfof enriching vapor required, even atpressures close to atmospheric, condensation starts at temperatures ofF. as compared to approximately 24 F. for a Cs hydrocarbon such ashexane.

The cracking portion of the feedstock should not contain lanyappreciable concentration of a hydrocarbon heavier than C9 primarilybecause a heavier hydrocarbon tends to deposit excessive amounts ofcarbon under the conditions of partial oxidation with resultant foulingof the catalyst in the cracking tubes. Generally speaking, one of theobjects of the invention is to maintain the activity of the catalyst ata high level for long periods of time, such as seven days or more, afterwhich the initial activity can be restored in less than two hours byreactivation with air or mixtures of air and steam.

The B. t. u. and specific gravity of the partially oxidized product gasas it comes from the cracking operation are controlled to apredetermined value by adjusting the steam to air ratio in the mixturefed to the catalytic cracking tubes; the heating value can be variedover a range of to 370 B. t. u. and the specic gravity from 0.35 to 0.71as compared to air. Cold enrichment of this product gas with theenriching portion of the feedstock results in a finished gas of thedesired B. t. u. value and specic gravity as will now be readilylunderstood.

(Air Gas from Pentane) 2C|Hu 5031+ 18.8Nz=10C0 12H2 18.8Nz 8 l' (SteamGas from Pentane) C5Hi2+5HzO=5CO+11Hz A more complete understanding ofthe invention may be had from the following description of a typicalplant for the practice of the process.

In the accompanying drawings forming part of this specification, Fig. lis a diagrammatic view of a plant for the practice of the presentinvention. Figs. 2 and 3 are explanatory charts.

A plant constructed in accordance with the present invention comprises astill or fractionating column I of any preferred type for dividing theselected gasoline feedstock into the fractions already mentioned,namely, an enriching portion, a cracking portion, and a still bottomresidue suitable for use as fuel oil or motor fuel. The plant alsocomprises a catalytic cracking furnace II wherein the cracking portionof the feedstock is catalytically cracked i, e., partially oxidized withan oxidizing agent such as steam and/or air to produce a product gasrich in hydrogen and carbon monoxide.

A storage vessel for the gasoline feedstock to be processed is indicatedat I2. The feed line I3 to the still I0 includes a pump I4, a controlvalve I 5, and a heat exchanger I6.

The still bottoms residue is withdrawn from the still IIJ by a pump Ilwhich delivers to a line 20, 2l which leads through the heat exchangerI6 and thence by line 23, 24 to burners 22 which heat the catalyticcracking furnace I I. A branch 25 at the junction of lines 23 and 24delivers the excess fuel to storage or for other uses.

Heat for the fractionating of the feedstock in the column I0 may besupplied in any preferred way as by continuously withdrawing andreheating a portion of the still bottoms residue in a reboiler 26 towhich a. feed line 21 delivers and from which a return line 30 extends.

The distillate coming from the still I0 is conducted by an overhead line3I to a water-cooled condenser 32 where the heavier hydrocarbons arecondensed, the condensed portion constituting the cracking portion ofthe feedstock. The vapors which do not condense constitute the enrichingportion of the feedstock. From the condenser the condensate anduncondensed vapors flow to an accumulator 33. From the accumulator, theuncondensed vapor iiows through line 34, 35 to a mixing chamber 36. thesaid line having a control valve 31.

The condensate in the accumulator 33 is drawn therefrom by a pump 40which delivers to two separate lines 4I and 42. A portion of thecondensate is or may be returned to the still as reflux through line 4Iwhich includes a control valve 43. The setting of the valve 43 iscontrolled by a reflux ratio iiow controller 44 which in turn iscontrolled by the metering orifice 45 in the feedstock line between thestorage vessel I2 and the still. The remaining portion of thecondensate, the cracking portion, ows through line 42 to a heatedvaporizer 46 and thence to a mixing chamber 41 by way of a line 50having a control valve I. Steam and air supply lines 52 and 53,respectively, also deliver to said mixing chamber 41. The setting'of thecontrol valve 5I is controlled by a controller 54 which in turn is con-4 trolled by a metering orifice 65 in the finished gas line 56. In themixing chamber 41 the cracking Portion of the feed stock is mixed withsteam and/or air in controlled proportions preparatory to beingcatalytically cracked or oxidized. The cracking furnace I I comprises aplurality of vertically disposed cracking tubes 51 arranged in laterallyspaced relation in a heating chamber heated by the burners 22 which firedirectly thereinto. The cracking tubes will ordinarily be made of aheat-resisting alloy and will ordinarily contain a divided catalyticmaterial such as broken pieces of flrebrick impregnated with nickelnitrate or any other suitable catalyst. Before entering the crackingtubes the mixture from the mixing chamber is preheated in a preheater60. The cracking temperature is preferably above 1600 F.

From the cracking tubes the product gas iiows to a cooler 6| where it iscooled to atmospheric temperature and thence to the mixing chamber 36where it is cold enriched with the enriching portion of the feed stock.The quantity of enriching vapor added at 36 is controlled by aninstrument 62 known in the trade as a Calorimixer," this instrumentcontrolling the setting of the valve 31 in the enriching vapor feed line34, 35, the instrument itself being responsive to the B. t. u. value ofthe finished gas in the nished gas line 56.

A typical analysis of the partially oxidized product gas is: CO2, 4.6%;CO, 23.0%; H2, 44.6%; CH4, 6.8%; N2, 21.0%-B. t. u. 288 and specificgravity of 0.57 compared to air at 1.0.

A typical analysis of the enriched product gas which can be used inplace of a typical city gas of 540 B. t. u. and 0.68 specific gravityis: CO2, 4.2%; CO, 21.2%; H2, 41.0%; CHi, 6.3%; CiHm, 8.1%; N2, 19.2%.

The pressure in the accumulator 33 and the still or fractionating columnI0 is controlled by a pressure controller 63 which is responsive to thevapor pressure in line 34. This controller controls the setting of avalve 64 in the water outlet line 65 from the condenser 32 and controlsthe quantity of cooling water fed to the latter through line 66.

The composition of the product gas from the cracking tubes 51 can bevaried by varying the steam to air ratio in the hydrocarbon-steam-airmixture fed to said tubes from 41. For the purpose of illustration thechart in Fig. 2 is included to show the typical variations incomposition, heating value and specific gravity of these product gasesproduced from pentane without cold enrichment when going from steam-gasto 100% air-gas, i. e., from infinite steam-air ratio to zero steam-airratio. For further illustration the chart in Fig. 3 is included to showthe typical variations in heating value and specific gravity of chartFig. 2 gases when cold enriched with butane. Chart Fig. 3 alsoillustrates the variations in composition of a 1000 B. t. u. finishedgas produced from catalytically oxidized pentane enriched with butanewhen the steam-air ratio is varied from infinity to zero.

It will now be apparent that the method herein disclosed offers asolution to the heretofore very difficult problem of handling andtransporting the light petroleum fractions usable for the production andenrichment of fuel gases. By dissolving these light petroleum fractionssuch as Ce and lighter into the heavier fractions Cn to Ce it is nowpossible to handle and transport the solvent and solute in the samemanner as ordinary gasoline and when these components arev fractionatedfollowed by partially oxidizing the heavier and enriching with thelighter a stable fuel gas is now obtainable comparable andinterchangeable with city gas.

It is believed that from the foregoing the process will be clearlyunderstood by those skilled in the art. It will also be understood thatchanges may be made in the details disclosed without departing from thespirit of the invention as set forth in the appended claims.

What is claimed as new is:

l. A process of making fuel gas, which comprises the steps of (A)passing through a distillation zone a. petroleum feedstock selected fromthe group consisting of straight run gasoline and natural gasoline whosevapor pressure does not exceed 26 pounds Reids vapor pressure so as todivide the feedstock into three portions by fractional distillation,said portions being portion (l) comprised essentially of hydrocarbonslighter 'than Ce, portion (2) comprised essentially of C to Cahydrocarbons, and portion (3) comprised essentially of hydrocarbonsheavier than Cn; (B) passing portion (2) directly from the distillationzone to and'through a catalytic cracking zone and reacting it thereinwith an oxidizing agent of the class consisting of air, steam andmixtures thereof so as to produce a. product gas rich in hydrogen andcarbon monoxide; and (C) passing portion (1) directly from thedistillation zone into said product gas at a point adjacent the outletof the catalytic cracking zone so as to enrich the product gas of step(B) 2. A process of making fuel gas, which comprises the steps of (A)passing a petroleum feedstock selected from the group consisting ofstraight run gasoline and natural gasoline whose vapor pressure does notexceed 26 pounds Reids vapor pressure through a still so as to strip offa fraction comprised essentially of hydrocarbons at least as light asCn; (B) passing the stripped fraction in vapor form directly to andthrough a condensing zone vso as to divide the stripped fraction intotwo portions, said portions being a vapor portion (l) comprisedessentially of hydrocarbons lighter than Ca and a condensed portion (2)comprised essentially of Ca to Ca hy drocarbons; (C) passing portion (2)directly from the condensation zone to and through a catalytic crackingzone and reacting it therein with an oxidizing agent of the classcomslsting of air, steam and mixtures thereof so as to produce a productgas rich in hydrogen and carbon monoxide; and (D) passing portion (l)directly from the condensation zone into said product gas at a pointadjacent the outlet of the catalytic cracking zone so as to enrich theproduct gas of step (C).

3. A process `of handling light petroleum fractions for'use in themanufacture of fuel gas. which comprises the steps of (A) dissolving apetroleum fraction of hydrocarbons lighter than Cs in a petroleumfraction comprised essentially of C9 to Ca hydrocarbons, for purposes ofstorage and shipment; (B) passing the solution of petroleum fractionsobtained in step (A) through a. distillation zone so as to divide thesolution into two portions by fractional distillation, said portionsbeing portion (1) comprised essentially of hydrocarbons lighter than Ceand portion (2) comprised essentially of C9 to Cs hydrocarbons: (C)passing portion (2) directly from the distillation zone to and through acatalytic cracking zone and reacting it therein with an oxidizing agentof the class consisting of air, steam and mixtures thereof so as toproduce gas rich in hydrogen and carbon monoxide; and (D) passingportion (l) directly from the distillation zone into said product gas ata point adjacent the outlet of the catalytic cracking zone so as toenrich the product gas of step (C).

CHARLES GORDON MILBOURNE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,235,777 marea et a1 Aug. 7.1917 1,967,669 Hickey' July 24, 1934

1. A PROCESS OF MAKING FUEL GAS, WHICH COMPRISES THE STEPS OF (A)PASSING THROUGH A DISTILLATION ZONE A PETROLEUM FEEDSTOCK SELECTED FROMTHE GROUP CONSISTING OF STRAIGHT RUN GASOLINE AND NATURAL GASOLINE WHOSEVAPOR PRESSURE DOES NOT EXCEED 26 POUNDS REIDHS VAPOR PRESSURE SO AS TODIVIDE THE FEEDSTOCK INTO THREE PORTIONS BY FRACTIONAL DISTILLATION,SAID PORTIONS BEING PORTION (1) COMPRISES ESSENTIALLY OF HYDROCARBONSLIGHTER THAN C6, PORTION (2) COMPRISED ESSENTIALLY OF C9 TO C6HYDROCARBONS, AND PORTION (3) COMPRISED ESSENTIALLY OF HYDROCARBONSHEAVIER THAN C9; (B) PASSING PORTION (2) DIRECTLY FROM THE DISTILLATIONZONE TO AND THROUGH A CATALYTIC CRACKING ZONE AND REACTING IT THEREINWITH AN OXIDIZING AGENT OF THE CLASS CONSISTING OF AIR, STEAM ANDMIXTURES THEREOF SO AS TO PRODUCE A PRODUCT GAS RICH IN HYDROGEN ANDCARBON MONOXIDE; AND (C) PASSING PORTION (1) DIRECTLY FROM THEDISTILLATION ZONE INTO SAID PRODUCT GAS AT A POINT ADJACENT THE OUTLETOF THE CATALYTIC CRACKING ZONE SO AS TO ENRICH THE PRODUCT GAS OF STEP(B).